Crystallite structure of Palm shell Activated Carbon/MgO and Its Influence on Carbon Monoxide and Carbon Dioxide Adsorption

Abstract

Gas emission of the motor vehicle is a major contributor to climate change, with a
total of 14% emission annually, and the best potential option for reducing pollution is using the
adsorption method. Magnesium oxide (MgO) has been proven as an effective adsorbent for
liquid and gases. The impregnation of MgO on porous structure increases the affinity toward
nonpolar gases, which is one of the purposes of this study. The crystallite structure is also a
key factor that determines the adsorption capacity of activated carbon (AC). However, deeper
analysis is needed in the activated carbon crystallite structure represented by d002 (aromatic
layer), Lc (crystallite height), and La (crystallite diameter) on the adsorption of motor vehicle
gas emissions. Three types of palm shell-based activated carbon were tested in this experiment.
The results showed that activated carbon made using the two-step method and the AC/MgO
produced surface structure with a d002 value of 0.33 nm and 0.32 nm, respectively. The
impregnation of MgO on AC showed changes in surface structure and affected its crystallinity.
The ability to adsorb CO2 and CO by AC/MgO increase up to 80% and 88%, respectively.

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Journal of Physics: Conference Series
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Crystallite structure of Palm shell Activated Carbon/MgO and Its
Influence on Carbon Monoxide and Carbon Dioxide Adsorption
To cite this article: Yuliusman and A R Nafisah 2021 J. Phys.: Conf. Ser. 1912 012027
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ICAMBF 2020
Journal of Physics: Conference Series 1912 (2021) 012027
IOP Publishing
doi:10.1088/1742-6596/1912/1/012027
1
Crystallite structure of Palm shell Activated Carbon/MgO
and Its Influence on Carbon Monoxide and Carbon Dioxide
Adsorption
Yuliusman and A R Nafisah
Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI
Depok, Indonesia
E-mail: azmiarizka@gmail.com
Abstract. Gas emission of the motor vehicle is a major contributor to climate change, with a
total of 14% emission annually, and the best potential option for reducing pollution is using the
adsorption method. Magnesium oxide (MgO) has been proven as an effective adsorbent for
liquid and gases. The impregnation of MgO on porous structure increases the affinity toward
nonpolar gases, which is one of the purposes of this study. The crystallite structure is also a
key factor that determines the adsorption capacity of activated carbon (AC). However, deeper
analysis is needed in the activated carbon crystallite structure represented by d002 (aromatic
layer), Lc (crystallite height), and La (crystallite diameter) on the adsorption of motor vehicle
gas emissions. Three types of palm shell-based activated carbon were tested in this experiment.
The results showed that activated carbon made using the two-step method and the AC/MgO
produced surface structure with a d002 value of 0.33 nm and 0.32 nm, respectively. The
impregnation of MgO on AC showed changes in surface structure and affected its crystallinity.
The ability to adsorb CO2 and CO by AC/MgO increase up to 80% and 88%, respectively.
1. Introduction
Indonesia is one of the countries with the highest percentage of air pollution in the world. Indonesia's
automobile growth has now increased by more than 10 percent every year, becoming a dominant
factor in air pollution. Vehicles produce dangerous gases such as carbon monoxide (CO) and carbon
dioxide (CO2). CO2 gas, in particular, is a major factor in global warming. To avoid extreme climate
change, carbon dioxide emissions should be reduced from 2050 cases to 41-72% worldwide.
Therefore, it is necessary to control environmental pollution. One of the ways that to reduce pollutants
in the air is the use of biomass waste as a material that can be converted into activated carbon.
Palm shell's solid waste has a high quantity, which is around 9% per base 1 tons of palm fresh fruit
bunches (FFB). So, there are 4.27 tons of biomass waste of palm shells per year. Previous research has
shown that the palm kernel shell used as a raw material can produce activated carbon with a good
surface structure with well-formed pores. The microporosity of activated carbon is highly dependent
on its microstructure, especially from the structure of the aromatic layer. The common method to
analyze the crystalline structure of activated carbon is using XRD. XRD has advantages such as
providing information and the quantitative value of the carbon structure with a wide range [1]. Crystal
structure parameters such as aromatic layer distance (d002), crystal height (Lc), and crystal diameter
(La) are used for carbon structure analysis [2]. These three parameters have been proven valid and
have also been used since the beginning of carbon structure research [3].

ICAMBF 2020
Journal of Physics: Conference Series 1912 (2021) 012027
IOP Publishing
doi:10.1088/1742-6596/1912/1/012027
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Another thing that can be used for improving the crystalline structure is metal oxide impregnation
to activated carbon. Metal oxides such as MgO, TiO2, BaO, CuO, and NiO have proven improving
pore structure and shape. Modification of activated carbon with CuO can increase the surface area of
BET to 658 m2/g with a ratio of 1: 1.5 [4]. MgO is also proven to have the ability to adsorb up to 43%
CO gas [5]. Modification with NiO can increase the total pore volume from 12% to 41% [6]. The
addition of metal will increase the active core so that the surface structure of the carbon changes and
the surface area and absorption capacity of activated carbon will increase.
Through this research, it is expected that metal oxide impregnation in activated carbon from palm
oil shells can change its structure and become an alternative solution to increase the absorption
capacity of motor vehicle gas emissions as an effort to improve air quality.
2. Experimental
2.1 Materials
There are three types of activated carbon used in this research. Two types of AC were made in the
previous research, i.e., two step carbon (TSC) and one step carbon (OSC). The specifications can be
seen in Table 1.
Table 1. Activated carbon used in this research
Types
Iodine number (mg/g)
OSC
584.48
TSC
1168.96
2.2 AC/MgO Synthesis
For the MgO modification, the TSC types were used. The steps for AC/MgO synthesis are descripted
below:
a. Dissolve 0.5 grams of MgO in 50 ml of distilled water to make a 1% w/v solution.
b. Put 50 grams of activated carbon into the MgO solution so that the ratio of activated carbon to
MgO is 1:1.
c. Stir the mixture of activated carbon and solution for 6 hours using a hot plate stirrer then let the
solution stand for 18 hours at room temperature.
d. Filter the modified activated carbon using filter paper and dry the modified activated carbon using
an oven at a temperature of 110 °C for 1 hour.
e. Carry out the reactivation process of modified activated carbon using a reactor by adjusting the
reactor temperature at a of 550 °C with a flow rate of N2 175 ml/min for one hour.
f. Remove the modified activated carbon from the reactor, put it in a closed sample container, and
store it in a desiccator.
The modified activated carbon (later was mentioned as TSC-M) was tested using iodine number
ASTM D4607-94 and also all the AC types were characterized using X-Ray Diffraction (XRD) which
determine the crystal structure, lattice parameters, and also the quantitative analysis.
2.3 Adsorption of CO and CO2
The CO2 and CO adsorption testing on motor vehicle emissions were carried out using a gas analyzer
type AGS 688. The testing process refers to SNI 19-7118.3-2005 for type L motor vehicles. The test
was done at normal temperature and atmospheric pressure. The scheme for adsorption process can be
seen in figure 1.
Furthermore, the percentage of motor vehicle emissions that had been adsorbed was calculated
based on the difference between the initial gas emission levels and the gas emission levels in the nth
minutes as shown in equation 1.
(1)

ICAMBF 2020
Journal of Physics: Conference Series 1912 (2021) 012027
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doi:10.1088/1742-6596/1912/1/012027
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Where:
G0 = initial gas emission level (% or ppm)
Gn = level of gas emission in the nth minute (% or ppm)
3. Results and discussions
The activated carbon of the TSC type was modified by using MgO. MgO has been recognized as a
type of oxide that can be used as an adsorbent with good adsorption ability. The addition of MgO to
AC can increase contact with the active core, thereby improve its performance [7]. Different from
other types of adsorbents, water vapor in the adsorbate gas mixture can be beneficial for the CO2 gas
adsorption process by MgO [8].
The TSC-M was tested using iodine number to predict the surface area. The iodine number of TSC-
M is 1005.31 mg/g. The TSC-M has a lower iodine number compared to the two other types of
activated carbon because MgO has filled micropores in carbon and increased its microporosity [9].
Because of this, the iodine number decreases, indicating a reduction in the surface area of the AC.
The three types of AC were then characterized using XRD. The peaks from XRD can be seen in
Table 2.
Table 2. XRD results
Types
kc
λ
2θ peak (°)
FWHM (nm)
OSC
0.94
1.54
24.13
0.30
0.94
1.54
29.98
0.19
0.94
1.54
31.23
0.50
TSC
0.94
1.54
26.63
0.13
0.94
1.54
29.07
0.56
0.94
1.54
42.79
0.21
TSC-M
0.94
1.54
23.35
0.09
0.94
1.54
42.67
1.19
0.94
1.54
61.90
1.91
The XRD test results were then processed using the Origin Pro 8.5 (OriginLab Corporation)
Software. The average crystallite size was calculated from the peak with the highest intensity in the
XRD pattern using the Scherrer equation [10]. Then the calculation of the cryptic parameter is carried
out with the Bragg Equation which is a derivative of the Scherrer equation. The diffraction angle 2θ
and FWHM value for the two planes (002 and 100) were obtained by the curve fitting method. From
these datas, calculations were made which include critical lattice parameters such as d002 (aromatic
layer), crystallite height (Lc), crystallite diameter (La), and the number of aromatic layers per carbon
crystallite (Nave) using the Bragg equation. The calculation results showed in Table 3.
Motorcycle exhaust
Outer tube
Inner tube
Figure 1. Adsorption Scheme

ICAMBF 2020
Journal of Physics: Conference Series 1912 (2021) 012027
IOP Publishing
doi:10.1088/1742-6596/1912/1/012027
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Table 3. Calculation of crystallite parameters
AC types
2θ002
2θ100
FWHM002
FWHM100
d002
(nm)
Lc
(nm)
La
(nm)
Nave
OSC
24.13
44.38
0.30
0.72
0.37
27.97
12.45
76.91
TSC
26.63
42.79
0.13
0.21
0.33
66.96
42.56
201.18
TSC-M
23.35
42.67
0.09
1.19
0.32
96.26
7.51
253.93
Commonly the d002 value ranges from 0.34 nm. The d002 values of the OSC and TSC-M samples
were slightly above the literature. This can be due to the irregular structure between layers [11]. The
second type of activated carbon, TSC, has a value of d002 which indicates that the TSC sample has a
crystallinity level comparable to graphite [12]. The decreasing d002 value indicates the distance
between the grains decreases, thus indicating an increase in the crystallinity of activated carbon.
From the adsorption test results, it can be seen that a significant increase in adsorption showed in
the three types of AC. But modified activated carbon gives the best results, which can reduce CO2 gas
emissions by up to 80%. The data is reflected in figure 2.
Figure 2. CO2 Adsorption test result
The adsorption capacity increases with increasing surface area of activated carbon. But in modified
activated carbon, there is an increase in adsorption capacity even though the surface area decreases.
This is caused by MgO which adds to the active site of the adsorbent. So, it can be concluded that the
ability of CO2 adsorption using activated carbon does not depend on the surface area, but rather on the
porosity and crystallinity of activated carbon [2]. The crystallinity of AC can be defined with the
lattice parameters mentioned before .
The adsorption process on activated carbon is predominantly physical adsorption. MgO supported
by activated carbon increases the dipole ion interaction between MgO and CO2. So that the texture
properties and surface chemical properties affect the CO2 absorption performance [13]. The carbon
will bind to the CO2 molecule which is influenced by Van der Waals forces. If the adsorption process
on activated carbon is generally physical adsorption, then the difference occurs in the CO2 adsorption
process on MgO. Several studies have shown that adsorption on MgO is more suitable using the
pseudo-second-order model wherein this model chemical adsorption is more dominant. The results of
the analysis using FTIR show that CO2 adsorption on MgO is dominated by chemical adsorption with
little physical adsorption [8].

ICAMBF 2020
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doi:10.1088/1742-6596/1912/1/012027
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The addition of MgO to activated carbon increases the polarity of the TSC-M sample so that this
type will be good for binding nonpolar CO2 gas. The chemical reaction between MgO and CO2 can
produce several bonds including unindents, bidentate carbonate, and bicarbonate types. Analysis
conducted on literature resulted in the conclusion that the majority of compounds formed as a result of
the reaction between CO2 and MgO are types of bidentate carbonate. MgO helps the formation of
hydroxyl radical compounds that are suitable for the adsorption of gases with non-polar properties
[14].
In the adsorption process using TSC-M carbon, there is contact with two surfaces, the metal oxide
surface, and the activated carbon. When the CO2 molecule comes into contact with the metal oxide
surface, there will be a direct carbonation process which is thermodynamically stable at ambient
temperature and pressure conditions [15]. Also, the insertion of MgO increases the affinity for CO2
[13]. MgO can adsorb CO2 gas at room temperature which is good and proven to be effective. Based
on the rate-limiting model, the CO2 adsorption process on MgO is controlled by two things, film
diffusion, and intraparticle diffusion. At the beginning of the adsorption process, the resistance from
the diffusion of the film will regulate the adsorption rate. Then proceed with intraparticle diffusion
resistance which is the main factor in the subsequent adsorption rate [8].
When the CO gas flow starts to hit the AC surface, the CO molecules will be adsorbed on the outer
surface of the adsorbent at low pressure and gradually enter the inside of the adsorbent. In general, an
increase in temperature will increase the ability of AC to adsorb CO gas. So, at standard pressure, CO
gas is only adsorbed in the outer of adsorbent [16]. The results for CO adsorption showed in figure 3.
Figure 3. CO adsorption result
From this study, it is understood that the ability of activated carbon to adsorb CO2 is better than
CO, although the adsorption percentage of CO gas is higher because the initial content of CO gas in
motor vehicle emissions is not as high as CO2 gas. Simulations conducted by Lithoxoos show that the
best ability of activated carbon to adsorb several types of gases is CO2, CH4, then CO, respectively
[17]. One of the factors found prominent was the density profile of each adsorbate molecule. The
density profile simulation results show that the majority of the adsorbed gas molecules are distributed
near the pore walls. Besides, CO gas diffuses faster at high temperatures when CO2 gas can diffuse
more rapidly at room temperatures.
Based on the XRD results, the TSC-M carbon type has the smallest crystal size compared to other
types. The small crystal size makes intraparticle diffusion more even. So, this shows that the
crystallinity of carbon affects the adsorption of CO2 and CO gases. The Nave value of TSC-M is the
highest among others and showed the best performances for adsorption. Also, the crystallite height

ICAMBF 2020
Journal of Physics: Conference Series 1912 (2021) 012027
IOP Publishing
doi:10.1088/1742-6596/1912/1/012027
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(Lc) proportional to the Nave value. This correlation might affect the adsorption process. But these
matters are not certain yet and more research are needed for deeper analysis.
Carbon material plays an important key to improving environmental quality and also useful for
other needs. Making activated carbon by paying attention to the crystallinity structure is one thing that
can be done to get activated carbon that suits your needs. Good crystallinity of carbon can improve the
quality of activated carbon so that this material is a promising material in the future.
4. Conclusion
In this paper, the structure of modified activated carbon was analyzed using X-ray Diffraction (XRD)
method. MgO modified activated carbon (TSC-M) has the best adsorption of CO2 and CO in motor
vehicle emissions up to 80% and 88%, respectively, compared to the other AC types. The increase of
aromatic layer and crystallite height are affecting the AC adsorption ability.
Acknowledgments
This work is financially supported by the Directorate General of Higher Education, Ministry of
Education and Culture, Republic of Indonesia through the master's grant. Authors also thankful for all
the support from colleagues.
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